A. Technical Field
The present invention relates to an apparatus and a process for producing (meth)acrylic acid.
B. Background Art
It is a general industrial practice to produce (meth)acrylic acid by catalytic gas phase oxidation. However, (meth)acrylic acid is very easily polymerizable, therefore there is a possibility that its polymerization often might occur in its production process and, as a result, it might become impossible to continue the operation.
Usually, polymerization inhibitors such as hydroquinone, phenothiazine, hydroquinone monomethyl ether, diphenylamine, copper dialkyldithiocarbamates, N-oxyl compounds and molecularoxygen-containing gases are used in order to inhibit the polymerization of (meth)acrylic acid in its production process, or the inner wall surface of the apparatus is treated in order to prevent solid materials, such as polymers and deposits, from attaching to the apparatus.
However, even the use of the polymerization inhibitor or the inner wall surface treatment for the apparatus still results in insufficient inhibition of the polymerization of (meth)acrylic acid.
A. Object Of The Invention
It is an object of the present invention to provide an apparatus for producing (meth)acrylic acid and a process for producing (meth)acrylic acid with this apparatus wherein the apparatus enables to produce (meth)acrylic acid stably for a long period of time by effectively inhibiting the polymerization of (meth)acrylic acid in its production process.
B. Disclosure Of The Invention
SUS316 stainless steel (molybdenum content=2.0 to 3.0 mass %, copper content=0 mass %) is usually used for the apparatus for producing (meth)acrylic acid. However, by the present inventors"" studies, it has been found that apparatuses made of stainless steel with a low molybdenum content such as SUS316 are liable to involve the polymerization of (meth)acrylic acid, and that much polymerization occurs particularly in reboilers of distillation columns in which (meth)acrylic acid is exposed to severe conditions, and further that the polymerization of (meth)acrylic acid can effectively be inhibited by replacing the SUS316 with a nickel-chromium-iron alloy having a high molybdenum content or containing copper even if the molybdenum content is low. The present invention has been completed on the basis of such findings.
That is to say, the present invention provides an apparatus for producing (meth)acrylic acid by catalytic gas phase oxidation, wherein at least a part (particularly, a part coming into contact with (meth)acrylic acid) of the apparatus is made of:
(A) a nickel-chromium-iron alloy with a molybdenum content of 3 to 20 mass %, but not including 3 mass %; or
(B) a nickel-chromium-iron alloy with a molybdenum content of 1 to 4 mass % and a copper content of 0.5 to 7 mass %.
The present invention further provides a process for producing (meth)acrylic acid, in which (meth)acrylic acid is produced with the above apparatus according to the present invention.